This invention concerns treatment of wet age-related macular degeneration (AMD) in the eye, and in particular concerns use of radiation to treat such macular degeneration, the radiation being administered from behind the sclera. Treatment of ocular tumors also forms a part of the invention.
Wet age-related macular degeneration has been the leading cause of blindness in the United States, and a leading cause in the world. It is characterized by the growth of abnormal blood vessels from the choroidal membrane at the back of the eye, in the macular area of the retina including the fovea and immediately surrounding regions. This is called “choroidal neovascularization” (CNV). The term “wet” refers to the fact that these abnormal blood vessels leak and damage the macula, causing central vision distortion. Thus, the highest resolution vision of the patient is severely compromised or lost.
Approximately ten percent of AMD cases comprise wet AMD, and this is the type which can lead to blindness. Dry AMD comprises approximately ninety percent of AMD cases, but a certain percentage of these (approximately ten percent) eventually progress to wet AMD.
Of wet AMD patients, approximately seventy percent of these cases are classic wet AMD, while approximately thirty percent are what is known as occult AMD. In both cases CNV occurs, invading the choroid and the space above the choroid with proliferating blood vessels which cause damage. In the case of classic AMD, the new blood vessels remain essentially intact, while in occult AMD the blood vessels leak, form a somewhat amorphous mass, and obscure the ability of a physician to see the vessel through an ophthalmoscope. Thus, any treatment aimed specifically at these vessels, requiring visual identification and location of the vessels, fails for occult AMD.
There have been several approaches to treatment of wet AMD. In both photodynamic therapy (PDT) and transpupillary thermal therapy (TTT) laser beams are used, directed through the front of the eye. These have had varying degrees of effectiveness, with PDT generally being the more effective of the two. In PDT, the treatment consists of a administering photosensitizing dye followed by laser treatment, which sensitizes the dye to affect the CNV condition. Results of both TTT and PDT have been less than ideal. With PDT, based on one study, only 15% of AMD patients would meet the Macular Photocoagulation Study Group (MPSG) guidelines for treatment; thus, most AMD patients would not benefit from this treatment. In addition, the cost for this treatment has been extremely high and its cost effectiveness is in question.
It is also noted that although the FDA recommends PDT treatment of patients with predominantly classic choroidal neovascular lesions from AMD, in most cases neovascularization recurred within three months. Thus, patients will probably need three to four treatments per year for this therapy to be effective, and the treatment basically preserves vision rather than improves visual acuity.
Researchers have discovered that x-ray radiation can be effective in treating CNV. Radiation has been administered from external sources, through the temple area, and also via brachytherapy using “plaques” which support radioisotope pellets, these plaques being implanted onto the back side of the eye, against the sclera, by insertion around the exterior of the sclera. These implanted plaques have been left in position for a prescribed duration of time, e.g. about 30 hours, or a range of about 18 to 65 hours, the time necessary to derive a radiation dose of about 17 Gy. Results of one study showed stabilization or sight improvement in about 45% of treated patients. After a seven year follow up, no sight-limiting radiation complications were noted in any patients. Thus, x-ray radiation, particularly administered by brachytherapy, is known to have some efficacy in the stabilization and improvement of the CNV condition of macular degeneration.
U.S. Pat. No. 6,443,881, issued to Paul Finger, describes use of these plaques and methods for locating the plaques using light sources mounted on the plaques.
External beam treatment is difficult and generally limited to highly specialized practitioners, with capital cost for equipment very high. This treatment is difficult for several reasons, including inability to produce a very small beam specific to the target, location of the beam precisely on the target, radiation damage to other structures, including brain tissue, and avoidance of irradiating the optic nerve and retna.
In addition to other limitations discussed above, the use of isotopes is not ideal. They are extremely limited as to choices of specific activity of the isotopes, as well as energy. Further, the isotopes must be shielded during emplacement for brachytherapy, as well as shielded directionally to protect adjacent structures, since the isotopes are isotropic emitters.
A much improved treatment for CNV of macular degeneration would be a controllable x-ray source which can be placed minimally adjacent to the macula, with accurate placement, with reliably accurate directional emission, and which can be controlled as to depth of radiation penetration as well as dose. These are objects of the present invention described below.